To lose this vivid, action-filled tone-poem of a painting from our public collections would be "like the Louvre not having the Mona Lisa", according to the National Gallery curator Carol Plazzotta. And a host of Britain's most prominent artists, from Sir Peter Blake to Paula Rego, are in passionate agreement.

Plazzotta was referring to Titian's Diana and Actaeon, which will be lost to the nation unless £50m is raised by the end of the year. She was speaking at the National Gallery in London as the work, which has not left Edinburgh since 1945, was reunited with its companion piece, The Death of Actaeon, for the first time in 200 years.

Speaking in support of the public appeal, Blake said: "This should be thought of separately from the recession. We shouldn't be thinking of not doing this when there is so much money in the art world, so many rich people."

Patrick Brill, better known by his pseudonym Bob and Roberta Smith, echoed him: "If we can spend £50bn on nationalising our banks, we ought to be able to nationalise this painting for £50m."

Diana and Actaeon is one of two Titians that, having been on long-term loan to the National Galleries of Scotland, are now being sold by the Duke of Sutherland. If the galleries fail to raise the £50m, it could be sold privately.

One firm pledge of £1m has been made by the Art Fund charity. Nicholas Penny, director of the National Gallery, said: "If we thought it was a hopeless case, we wouldn't have gone to the trouble of bringing Diana and Actaeon here. If we were all the way there, we wouldn't have done it either."

John Leighton, director general of the National Galleries of Scotland, said the Scottish government had been "very supportive, but I can't say how that will translate into pounds and pence". He said discussions with Westminster were "proceeding in a positive way".

Diana and Actaeon and The Death of Actaeon are part of a suite of works made by Titian for Philip II of Spain. The Death of Actaeon finishes the story that Diana and Actaeon starts. The hunter, who has seen the goddess naked in the first work, is vengefully torn to shreds by his own hounds in the second.

The painter Paula Rego said of Diana and Actaeon: "It's a very wonderful work of art, and a marvellous piece of revenge on her part. When we get to The Death of Actaeon, it's rather extreme. She's almost showing off her beauty while he is being chewed up. That's rather pleasing to me."

Diana and Actaeon and The Death of Actaeon can be seen at the National Gallery until the end of November.